XPS 15 battery charges to only 99%

My Dell XPS battery charges only to 99%. Technical support said this is a "normal" occurrence if you have "adaptive" charging on in the BIOS. They asked me to update the BIOS and then change it to "custom" charging. The battery now charges to 100%.

Is this normal behaviour or just a messy "fix"? I just want to confirm if this is a papered over fault, because I suspect that it is. Personally I am not too pleased with having to call Dell technical support on the day I opened my new laptop!